Which sequence of state transitions is INCORRECT in accordance with the following description?

Which sequence of state transitions is INCORRECT in accordance with the following description?

To provide for disaster recovery, a system (designated as A) has been provided with a backup system (designated as B). Only one of them can be active at a time. When A goes down, B becomes active. When A comes back up then B becomes inactive and A becomes active again. However, when A is down and B also goes down then a message is sent to the system administrator. After this once A comes back up, A becomes active or if B comes up then B becomes Active.